The subject matter disclosed herein relates to radiographic imaging, in particular, to a digital radiographic detector utilizing a continuous readout mode of operation.
It may be desirable to run wireless, portable digital X-ray detectors without any wired connections between the detector and the X-ray generator or the host computer, which manages the image acquisitions and the generator. One method for such a simplified interface is to continuously read out the detector and detect beam turn-on based on the content of the images, and then add all frames which contain image information. A critical part of this concept is the reliable real-time detection of when the beam-on and beam-off events occurred. A number of dark images may be captured and averaged. A current image frame may be compared line by line with the cumulative averages of dark images, and if a difference threshold between them is exceeded, beam-on is established. However, for tightly collimated images, the signal in the image area may be low enough such that the beam-on may not be detected in every case.
In other instances, external electromagnetic interference and other noise sources may cause an increase in row noise which can cause false triggers. Missed or false beam-on and beam-off events would have the following consequences. If the beam-on event is detected one frame late, some image information is potentially missed, which may cause image artifacts and require a re-take of the X-ray image. False triggers for the beam on event create a nuisance for the operator and might temporarily disable image captures. If the beam off event is detected one frame too early some image information is potentially missed, which may also cause image artifacts and require a re-take of the X-ray image. If the beam off event is completely missed, this can be mitigated by a time out but the image access time increases.
Neither of these conditions is desirable, which requires that the algorithms for beam-on and beam-off detection be as robust as possible, while still allowing real-time processing on the detector. Another problem with beam detection by continuous readout is that there is some additional dark signal in the images during the period, when the beam is on. This is caused by parasitic capacitance between the photodiodes and the data line as explained herein.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.